The present invention relates to underground or underwater antennas which are used for transmitting electromagnetic waves underground, underwater or in the inside of a concrete structure, or receiving electromagnetic waves from underground, underwater or the inside of the concrete structure by causing such antennas to be buried in, contacted or approached in the underground, underwater or concrete structure.
A conventional underground antenna is constructed as shown in FIG. 9 wherein elements (6) are supported in a metal casing (2) by means of a support member (4). Transfer wheels are mounted on the casing (2), and only a surface in contact with a ground (10) is open. The electromagnetic waves transmitted from the antenna elements (6) are radiated once into the air and are caused to come to the underground.
As underground radar, it has been hoped recently for an underground (underwater) antenna to be used for investigating correctly the location and condition of city water pipes, gas pipes, sewage pipes, electric wires buried underground, or measuring bearing power of the soil by the condition of echoes from the underground, or the discovery of an underground water vein. Furthermore, it has been desired to obtain an antenna that can be used for discovering pinholes in materials such as water or concrete columns and the like or for reception of electromagnetic waves coming from the underground efficiently in order to forecast earthquakes. Still furthermore, it has been desired to provide an antenna capable of detecting land mines and living body reactions of a person buried in tiles and pebbles at a calamity or a person buried in snow at a snowslide. Heretofore, when an electromagnetic wave enters into the ground or another physical body, as described in the foregoing, an aerial antenna for use above the ground is brought into practice, but because of the adoption of irrational methods such as forcing the electromagnetic wave into the ground by all means, its efficiency is poor, and moreover, there is still another problem in that this antenna does not function normally even if it is buried in the underground. Furthermore, a study has been conducted to make use of the electromagnetic waves (electric wave, electric field, magnetic field) coming from a source of earthquake when an earthquake occurs by receiving the waves with an aerial antenna above ground to forecast the earthquake. However, in the air, a variety of electromagnetic waves (artificial noise, natural noise) are in existence, and this presents a rather difficult problem.